1. Field of the Invention
The present invention relates to a process for producing a magnet, and more specifically it relates to a process for producing a rare earth magnet containing a rare earth element.
2. Related Background Art
Rare earth magnets with R—Fe—B (=rare earth element) based compositions exhibit excellent magnetic properties, and much research is being devoted to further improving their magnetic properties. Residual flux density (Br) and coercive force (HcJ) are generally used as indices of the magnetic properties of magnets. It is known in the art that the HcJ value of a rare earth magnet can be improved by adding Dy or Tb.
However, since the saturation magnetization of an R—Fe—B based compound is lowered when an element such as Dy or Tb is selected as R, its addition in an excessive amount will tend to reduce the Br value. A method for minimizing this inconvenience has been disclosed in International Patent Publication No. WO2006/043348, wherein a sintered magnet having an R—Fe—B based composition is subjected to heat treatment at a temperature below its sintering temperature while a powder containing an oxide, fluoride or oxyfluoride of a rare earth element is present on its surface. Also, Japanese Patent Application Laid-open No. 2005-285860, Japanese Patent Application Laid-open No. 2005-285861 and Japanese Patent Application Laid-open No. 2005-209932 disclose processes for producing rare earth magnets by dipping a magnet element in a molten alloy composed mainly of a rare earth element.